Sprint's newest smartphone — the HTC Evo 4G — can rocket you to the newest, zippiest mobile data networks in the U.S., but at a huge strain on battery life.

The Evo — a handset launching June 4 that's based on Google's Android mobile operating system — is billed as America's first 4G, or fourth-generation, phone, with speeds up to 10 times faster than current 3G networks.

I put those claims to the test in Philadelphia, one of just 32 U.S. markets to initially offer 4G wireless (with more coming by year's end).

Bottom line: Evo was usually faster in the City of Brotherly Love compared with the non-4G areas I tested it in, including northern New Jersey, suburban Detroit and Miami Beach. But 4G speeds were inconsistent and didn't approach the upper reaches of Sprint's claims.

The more concerning issue was the battery. It pooped out after only a few hours of general use, or well before the business day had ended. (To be fair, my iPhone 3G battery failed around the same time.)

Sprint concedes that searching for and using 4G is a drain, and that you'd want to disable 4G and revert to 3G when the faster network isn't available. Of course, turning off 4G when you are in high-speed territory partly defeats the purpose of having such a device in the first place.

Still, Evo functions as a very respectable, feature-rich 3G-based smartphone.

Indeed if you are able to stay juiced up, the Evo is an attractive piece of hardware. It costs $200 after a rebate and with a two-year Sprint contract. An unlimited data plan with 450 voice minutes and 4G access costs $80 a month.

Here's a closer look:

•Appealing specs. Apart from speed, Evo has a lot going for it, starting with an inviting 4.3-inch multitouch display that's much larger than you usually find on a smartphone. I had difficulty making it out in sunshine, though. Evo has an 8-megapixel autofocus camera with flash, plus a front-facing camera that Sprint says you'll be able to use for video chat (the software wasn't ready for testing). You can capture high-definition video (up to 720p) and watch on an HDTV by connecting an optional $30 HDMI cable directly to the phone.

For an extra $30 a month, you can use Evo as a mobile Wi-Fi hot spot for wirelessly tethering up to eight Wi-Fi-capable computers or other devices, a useful feature that worked fine in my tests.

Evo has most of the other accouterments of the modern smartphone, including Wi-Fi, GPS, sensors that change the orientation of the display depending on how you rotate it, and the ability to pinch or spread your fingers to zoom in on a Web page, map or photograph. It's loaded with such apps as Sprint TV and the Amazon MP3 store, and also has a handy kickstand on the back that you can use to prop up the device to watch video.

Moreover, as the device is based on Google's mobile operating system, you can access the Android Market online store with some 35,000 free or fee-based third-party apps. However, because of a limitation on the version of Android software used in the device, you can't store third-party apps on the 8-gigabyte microSD card that Sprint supplies. And just 358 megabytes of the 1 GB of internal memory is set aside for app storage.

Among other enhancements, Android version 2.2, which Google previewed last week, will address the SD card limitation; Sprint isn't saying when or if Evo might get a 2.2 makeover.

At 6 ounces, the handset is a little heavier than most rival smartphones, though I didn't mind the extra weight.

•The need for speed. For all the niceties, the reason you're reading about Evo is 4G. I received a notification that a 4G network was available as I approached Philadelphia on an Amtrak train. The results of my initial speed test — I used the Speedtest.net Android app — yielded download speeds just shy of 3 megabits per second, or about two to four times better than I had been getting with 3G. (Sprint says average 3G speeds are in the 600 Kbps to 1.4 Mbps range, which generally jibed with my results.) The initial 4G upload speeds of about 1 Mbps were marginally faster than I was getting with 3G.

Sprint says peak download speeds can exceed 10 Mbps, with an average of 3 to 6 Mbps. Mine topped out at 4.3 Mbps but bounced around a lot, dropping at times to a fraction of that speed. Several readings were in the 1 to 3 Mbps range. I achieved the fastest results around City Hall, compared with the 30th Street train station, where 4G was spotty. Alas, not long after I got to City Hall, I received my first low-battery warning and had to search for a power outlet. Indeed, as with many cellphones, you'll have to manage battery use carefully.

The raw numbers are one thing, of course, but it's what you can do as a result of faster speeds that really counts. When I had decent 4G coverage, surfing was snappy and downloads were quick. The quality of YouTube videos was dramatically superior — I could watch in HD. The Google Goggles visual search app worked its magic faster, too — you take a picture and Goggles generates a search based on the image.

Sprint may be out front on 4G, but it's not the only carrier banking on speed, an eventual boon for any smartphone user. For now, though, accessing a faster data network comes with a challenge: having ample juice to get through your day.

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